J. A. Manson
Lehigh University
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Archive | 1976
J. A. Manson; L. H. Sperling
(75) Inventors: Charles Wilson Colman, Marietta, GA (US); Rodney Lawrence Abba, Oshkosh, WI (US); Jaime Braverman, Altanta, GA (US); John Thomas Cooper, Clinton, TN (US); Maureen Myrl Falls, Neenah, WI (US); Tiffany Marshalle Lee Hunter, Stone Mountain, GA (US); Steven Rashad Inabinet, Knoxville, TN (US); David Martin Jackson, Roswell, GA (US); Nancy Donaldson Kollin, Roswell, GA (US); Yen-Ling Lai, Duluth, GA (US); Sylvia Bandy Little, Marietta, GA (US); Robert John Makolin, Neenah, WI (US); David Joseph Nickel, Neenah, WI (US) (73) Assignee: Kimberly-Clark Worldwide, Inc., Neenah, WI (US) Subject to any disclaimer, the term of this patent is extended or adjusted under 35 U.S.C. 154(b) byday.days.
Journal of Materials Science | 1977
M. D. Skibo; R. W. Hertzberg; J. A. Manson; S. L. Kim
Fatigue fracture surface characteristics of five commercially available amorphous polymers [poly(methylmethacrylate) (PMMA), polycarbonate (PC), poly(vinyl chloride) (PVC), polystyrene (PS), and polysulphone (PSF)] as well as bulk-polymerized PMMA prepared over a wide range of molecular weights were studied to determine if common mechanisms of fatigue crack propagation prevail among these glassy polymers. In those polymers with viscosity-average molecular weight ¯Mv≲2×105, the macroscopic appearance of the fracture surface showed the presence of a highly reflective mirror-like region which formed at low values of stress intensity and high cyclic test frequencies (∼100 Hz). The microscopic appearance of this region revealed that many parallel bands exist oriented perpendicular to the direction of crack growth and that the bands increase in size with ΔK. In all instances, the crack front advanced discontinuously in increments equal to the band width after remaining stationary for hundreds of fatigue cycles. Electron fractographic studies verified the discontinuous nature of crack extension through a craze which developed continuously with the load fluctuations. By equating the band size to the Dugdale plastic zone dimension ahead of the crack, a relatively constant yield strength was inferred which agreed well with reported craze stress values for each material. At higher stress intensity levels in all polymers and all values of ¯Mv, another series of parallel bands were observed. These were also oriented perpendicular to the direction of crack growth and likewise increased in size with the range in stress intensity factor, ΔK. Each band corresponded to the incremental advance of the crack during one load cycle, indicating these markings to be classical fatigue striations.
Journal of Materials Science | 1987
R. W. Lang; J. A. Manson; R. W. Hertzberg
Fatigue-crack profiles and fracture surfaces of several short glass fibre-reinforced polymers were examined to gain insight into the mechanisms of cyclic damage and fatigue-crack propagation in these materials. Several distinctly different features were noted between fracture surfaces generated by stable fatigue crack growth and those produced by monotonic or unstable fracture. Among the most significant differences were the higher degree of single and multiple fibre fracture generally observed on stable fatigue-crack growth fracture surfaces, and the variations in the interfacial failure site in well-bonded systems. While the former effect is attributed to the occurrence of crack closure and the build-up of compressive stresses in the crack-tip damage zone during unloading, the differences in the interfacial failure mode are related to the adverse effect of fatigue loading on the interfacial bond strength. No features could be identified that would allow a quantitative correlation between the applied stress intensity factor level or the crack growth rates and characteristic fracture surface details.
Journal of Materials Science | 1976
M. D. Skibo; R. W. Hertzberg; J. A. Manson
Fatigue crack growth characteristics in polystyrene were studied as a function of stress intensity factor range and cyclic frequency. Precracked single edge notched and compact-tension type specimens made from commercially available polystyrene sheet (mol.wt. =2.7×105) were cycled under constant load at frequencies of 0.1, 1, 10 and 100 Hz, producing growth rates ranging from 4×10−7 to 4×10−3 cm/cycle. For a given stress intensity level, fatigue crack growth rates were found to decrease with increasing frequency, the effect being strongest at high stress intensity values. The variable frequency sensitivity of this polymer over the test range studied was explained in terms of a variable creep component. The macroscopic appearance of the fracture surface showed two distinct regions. At low stress intensity values, a highly reflective, mirror-like surface was observed which transformed to a rougher, cloudy surface structure with increasing stress intensity level. Raising the test frequency shifted the transition between these areas to higher values of stress intensity. The microscopic appearance of the mirror region revealed evidence of crack propagation through a single craze while the appearance of the rough region indicated crack growth through many crazes, all nominally normal to the applied stress axis. Electron fractographic examination of the mirror region revealed many parallel bands perpendicular to the direction of crack growth, each formed by a discontinuous crack growth process as a result of many fatigue cycles. The size of these bands was found to be consistent with the dimension of the crack tip plastic zone as computed by the Dugdale model. At high stress intensity levels a new set of parallel markings was found in the cloudy region which corresponded to the incremental crack extension for an individual loading cycle.
Journal of Materials Science | 1973
R. W. Hertzberg; J. A. Manson
The fatigue-crack propagation characteristics in poly(vinyl chloride) (PVC) are examined in terms of fracture mechanics concepts where the crack growth rate is related to the applied stress intensity factor range. The microscopic details of fatigue crack extension are examined with the aid of light optical, scanning and transmission electron microscopes. The mechanism of crack advance is found to be that of void coalescence through craze material generated in advance of the crack tip. While the craze is shown to grow continuously with cyclic loading, the crack is found to grow discontinuously in several hundred cycle increments.
Journal of Materials Science | 1978
R. W. Hertzberg; M. D. Skibo; J. A. Manson
The fatigue crack propagation characteristics of a typical commercial homopolymer and copolymer polyacetal were determined. These materials were found to be the most fatigue resistant plastics examined to date, thus confirming the generally high fatigue resistance of all crystalline polymers. A discontinuous fatigue cracking process was identified at all test frequencies in the acetal copolymer and at high frequencies in the homopolymer, while continuous crack propagation occurred at low test frequencies in the homopolymer. The discrete advance increments of the crack in the discontinuous mode were equal to the dimension of the prevailing crack-tip plastic zone. On a more local scale, the crack path is seen to be mainly trans-spherulitic in nature.
Journal of Materials Science | 1990
W.-M. Cheng; G. A. Miller; J. A. Manson; R. W. Hertzberg; L. H. Sperling
A series of tensile and three-point bending studies was conducted at various temperatures and loading rates using a commercial poly(methyl methacrylate) (PMMA). Tensile properties and fracture toughness data were obtained for the various conditions. In general, both tensile strength and fracture toughness increase with increasing loading rate and decreasing temperatur E. However, when the temperature reaches the glass transition region, the relationships between fracture toughness, loading rate, and temperature become very complex. This behaviour is due to the simultaneous interaction of viscoelasticity and localized plastic deformation. In the glass transition region, the fracture mechanism changes from a brittle to a ductile mode of failure. A failure envelope constructed from tensile tests suggests that the maximum elongation that the glassy PMMA can withstand without failure is about 130%. The calculated apparent activation energies suggest that the failure process of thermoplastic polymers (at least PMMA) follows a viscoelastic process, either glass orβ transition. The former is the case if crack initiation is required.
Polymer | 1984
J Michel; J. A. Manson; R. W. Hertzberg
Abstract A simple theory is presented to explain the strong influence of molecular weight ( M ) on rates of fatigue crack propagation (FCP) in amorphous polymers. It is proposed that the equation describing FCP rates may be expressed as the product of two functions, one involving the stress intensity factor ( ΔK ), and the other characterizing the relaxation process occurring in the plastic zone. To provide a physical network in the plastic zone that can sustain fatigue loading, it is proposed that one needs a sufficient fraction of molecular fibrils per unit area ( W∗ ) whose lengths are greater than M c , the critical value of M required for entanglement. This effect can be summarized as a generalized rate process (confined at the plastic zone) expressed by A exp ( Bσ ) where σ is a stress and A and B are constants ( B including the volume of activation). It is deduced that M influences the activation volume through the values of W∗ and W , the weight fraction of molecules whose M > M c . Using the equation developed it was possible to correlate FCP data of PVC and PMMA as a function of M with a high degree of confidence. Also, the value of activation volumes obtained compared favourably with those in the literature for static tests. The complementary value of W∗ for these polymers was also seen to approximate closely to the void fraction in a craze. Extension to other cases such as semi-crystalline materials also seems possible.
Journal of Materials Science | 1981
Philip E. Bretz; R. W. Hertzberg; J. A. Manson
The effect of plasticization on the fatigue crack propagation response in polyamides was examined by conducting fatigue tests on specimens of nylon 66 (N66), nylon 6 (N6) and nylon 612 (N612) which had been equilibrated at various levels of absorbed water. In N66 and N6, crack growth rates decreased as the water content was increased to about 2.5wt%; with increasing moisture content, FCP rates increased and at saturation (8.5 wt% H2O) FCP rates were higher than those observed in the dry polymer. Crackgrowth rates in N612 decreased monotonically as the water content increased to saturation (3.2 wt% in this polyamide). These results were interpreted in terms of the competition between enhanced crack-tip blunting and lowering of the specimen modulus. Crack-tip blunting was believed to dominate fatigue behaviour at low water contents (⩽2.5wt%) and contributed to reduced FCP rates. The higher crack-growth rates observed at higher moisture levels were believed to be caused by reductions in material stiffness.
Archive | 1976
J. A. Manson; L. H. Sperling
This chapter concerns a diverse group of polymeric blends whose constituents may be either compatible or incompatible with each other. While the blends discussed in Chapter 3 are of interest because of their high impact strengths, the materials covered in this chapter are of interest because of a variety of other physical properties.